A coilbox provides an intermediate process in a hot strip mill in which a hot metal transfer bar is coiled at high speed from the roughing mill and then uncoiled at slow speed into the finishing mill. The head of the transfer bar enters the coilbox and is directed into the coiling area, where bending rollers drive and impart downward curvature, forming first the coil eye and then assisting additional coil wraps to be formed about the eye. A coil forming roller and a pair of driven cradle rollers support and contain the growing coil.
Uncoiling starts when the cradle rollers reverse coil rotation and a peeler forces open the outermost coil wrap, so as to feed the new head into a crop shear entry area and then toward the finishing mill. Uncoiling may involve active and/or passive coil transfer from the coiling area, through an intermediate uncoiling and transfer area, into a final uncoiling area.
The coilbox has revolutionized hot strip mill production of steel because it saves heat by accumulating long transfer bars between the roughing mill and the finishing mill. The coiling process reduces the surface area available for heat to radiate from the bar. This results in the uncoiled bar having virtually the same temperature as when it was coiled, allowing for near isothermal rolling without increasing the required rolling power. Also, the coiled bar is compact compared to the flat bar, which can save space and/or increase capacity of the mill. In addition to these primary benefits, the coilbox also provides further value by: equalizing cold skid-marks from walking beam furnace arrangements; breaking scale; allowing for the insertion of reheated coils; and acting as a temporary holding position before the finishing mill.
U.S. Pat. No. 5,310,131 describes initiating uncoiling of a coiled transfer bar at a first position with subsequent active transfer toward a second and final position without mandrels, using a system of coil cradles of two support rollers that are raised and lowered in opposition by pivoting the cradles, or a system of support rollers and a transfer ramp that are independently raised or lowered by pivoting of their respective frames. Both of these transfer mechanisms are complex, and therefore costly to build and to maintain.
U.S. Pat. No. 5,987,955 discloses an apparatus for active coil transfer from the coiling station to the uncoiling station without a mandrel, where two support rollers form a coil cradle to constitute the coiling station and two other support rollers form a coil cradle to constitute the uncoiling station. The coiling station rollers, and possibly the uncoiling station rollers, are differentially raised and lowered while remaining at a fixed distance from each other, so as to initiate the coil transfer into the uncoiling station, which itself has means for translating downstream from primary to secondary uncoiling positions. Because active transfer occurs by way of a bulk horizontal movement of the uncoiling station, there are regions of the transfer area where support rollers or aprons are periodically not present near the pass line. As a result, a turned down head or a passively transferring coil could fall into these open regions.
The object of the present invention is to address one or more of the disadvantages associated with known active transfer apparatus for use in hot strip mill coilbox assemblies.